1. Field of the Invention
The present invention relates to a communication system constructed by interconnecting a plurality of repeaters each having one or more devices connected thereto by a data transmission line and particularly to a communication method and a communication system capable of truly and precisely transmitting digital data from an input device to an output device having a different sampling rate from that of the input device.
2. Related Art
In recent years, digital audio equipment for recording and reproducing digitized characters, voice, image data or the like, such as CD (Compact Disk) drives, CD-ROM drives and DAT (Digital Audio Tape-recorder) units, have been rapidly widespread.
To record and reproduce original digital data (to be referred to as xe2x80x9coriginal dataxe2x80x9d hereinafter) truly and precisely, a sampling rate is set in each of these digital audio equipment.
A sampling rate of 44.1 kHz is used for CD drives, 32, 44.1 or 48 kHz for DAT units, 32 kHz for RDS (Radio Data System) units which provide character information service and automatic broadcast reception service by FM multiplex broadcasting, 44.1 kHz for digital audio amplifiers incorporating a DSP (Digital Signal Processor), and 44.1 or 48 kHz for MD (Mini Disc) drives.
There may be a request for transferring digital data from an output unit having a relatively low sampling rate to an input unit having a relatively high sampling rate, for example, transferring original data from an RDS unit having a sampling rate of 32 kHz to a digital audio amplifier having a sampling rate of 48 kHz to output voice, or transferring original data from a CD drive having a sampling rate of 44.1 kHz to an MD drive having a sampling rate of 48 kHz to be recorded.
In this case, it is conceivable to interpose an interface between the input unit and the output unit to carry out the processing of matching the sampling rates of these units.
That is, as a first method, interpolation is carried out on the original data, thereby making it possible to exchange digital data between input and output units having different sampling rates. As a second method, original data from an output unit is stored in a transmission buffer using a FIFO (First-In First-Out) system, DMA (Direct Memory Access) system or the like, the stored digital data is transmitted at a predetermined bit rate higher than the sampling rate of an input unit, the digital data received at this predetermined bit rate is stored in a receiving buffer, and the stored digital data is transmitted to the input unit at a transmission bit rate synchronized with the sampling rate of the input unit, thereby making it possible to exchange digital data between input and output units having different sampling rates.
However, when the former method is employed, unnecessary data other than the original data is interpolated for the original data, thereby making it difficult to transmit the original data truly and precisely.
When the latter method is employed, an interface including a control unit for controlling the timing of reading or writing digital data from or to the transmitting buffer, receiving buffer or transmitting-receiving buffer is required, and thus this interface has complicated circuit configuration and is expensive.
In view of the above situation, it is an object of the present invention to provide a transmission method and a transmission system in which digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input, by providing an interface having a simple and low cost circuit configuration between the input unit and the output unit.
To attain the above object, according to an aspect of the present invention, there is provided a transmission method, used in a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, the method comprising the steps of: setting a transmission reference clock which is the basis for an exchange of communication data between repeaters to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; setting a number of bits of each unit block of communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively, to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; modulating, by a repeater, device data to communication data synchronized with the transmission reference clock, when the device data synchronized with the device reference clock set in a source device connected to the repeater is output from the source device; adding a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation by the repeater; and transmitting the modulated communication data to a predetermined destination by the repeater.
According to the present invention, when a repeater receives the device data synchronized with the device reference clock set in a source device connected to the repeater from the source device, the repeater modulates the device data to communication data synchronized with the transmission reference clock; adds a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation; and transmits the modulated communication data to a predetermined destination by the repeater.
Therefore, by adding the phase information, the device data synchronized with the device reference clock set in the source device can be modulated to the communication data synchronized with the transmission reference clock without performing a processing of bit interpolation. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in the source device.
Further, to attain the above object, according to another aspect of the present invention, there is provided a transmission method, used in a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, the method comprising the steps of: setting a transmission reference clock which is the basis for an exchange of communication data between repeaters to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; setting a number of bits of each unit block of communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively, to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; demodulating, by a repeater, received communication data to device data synchronized with the device reference clock set in a destination device connected to the repeater, when the repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to the destination device; extracting a phase information added at the time of modulation by using an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation by the repeater; and transmitting, by the repeater, the demodulated communication data to the destination device.
According to the present invention, when a repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to a destination device connected to the repeater, the repeater demodulates the received communication data to device data synchronized with the device reference clock set in the destination device; extracts a phase information added at the time of modulation by using an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation; and transmits the demodulated communication data to the destination device.
Therefore, by extracting the phase information, the communication data modulated to synchronize with the transmission reference clock can be demodulated to the device data precisely synchronized with the device reference clock set in the source device without performing a processing of sinning bits. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in a source device.
Further, to attain the above object, according to still another aspect of the present invention, there is provided a transmission method, used in a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, the method comprising the steps of: setting a transmission reference clock which is the basis for an exchange of communication data between repeaters to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; setting a number of bits of each unit block of communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively, to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; modulating, by a repeater, device data to communication data synchronized with the transmission reference clock, when the device data synchronized with the device reference clock set in a source device connected to the repeater is output from the source device; adding a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation by the repeater; transmitting the modulated communication data to a predetermined destination by the repeater; demodulating, by the repeater, received communication data to device data synchronized with the device reference clock set in a destination device connected to the repeater, when the repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to the destination device; extracting the phase information added at the time of modulation by using the empty area which is equivalent to the difference between the number of bits of each unit block of the device data and the number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation by the repeater; and transmitting, by the repeater, the demodulated communication data to the destination device.
According to the present invention, when a repeater receives the device data synchronized with the device reference clock set in a source device connected to the repeater from the source device, the repeater modulates the device data to communication data synchronized with the transmission reference clock; adds a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation; and transmits the modulated communication data to a predetermined destination by the repeater. Conversely, when a repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to a destination device connected to the repeater, the repeater demodulates the received communication data to device data synchronized with the device reference clock set in the destination device;
extracts the phase information added at the time of modulation by using the empty area which is equivalent to the difference between the number of bits of each unit block of the device data and the number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation; and transmits the demodulated communication data to the destination device.
Therefore, by adding the phase information, the device data synchronized with the device reference clock set in the source device can be modulated to the communication data synchronized with the transmission reference clock without performing a processing of bit interpolation. Further, by extracting the phase information, the communication data modulated to synchronize with the transmission reference clock can be demodulated to the device data precisely synchronized with the device reference clock set in the source device without performing a processing of singing bits. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in the source device.
Further, to attain the above object, according to yet another aspect of the present invention, there is provided a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, each of the plurality of repeaters comprising: modulating means for modulating device data to communication data synchronized with the transmission reference clock, when the device data synchronized with the device reference clock set in a source device connected to the repeater is output from the source device, the transmission reference clock being the basis for an exchange of communication data between repeaters and being set to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; phase information adding means for adding a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation by the modulating means, a number of bits of each unit block of the communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively being set to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; and transmitting means for transmitting the communication data modulated by the modulating means to a predetermined destination.
According to the present invention, when a repeater receives the device data synchronized with the device reference clock set in a source device connected to the repeater from the source device, modulating means in the repeater modulates the device data to communication data synchronized with the transmission reference clock, and then phase information adding means adds a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation, and then transmitting means transmits the modulated communication data to a predetermined destination by the repeater.
Therefore, by adding the phase information, the device data synchronized with the device reference clock set in the source device can be modulated to the communication data synchronized with the transmission reference clock without performing a processing of bit interpolation. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in the source device.
Further, to attain the above object, according to further aspect of the present invention, there is provided a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, each of the plurality of repeaters comprising: demodulating means for demodulating received communication data to device data synchronized with the device reference clock set in a destination device connected to the repeater, when the repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to the destination device, the transmission reference clock being the basis for an exchange of communication data between repeaters and being set to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; phase information extracting means for extracting a phase information added at the time of modulation by using an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation by the demodulating means, a number of bits of each unit block of the communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively being set to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; and transmitting means for transmitting the communication data demodulated by demodulating means to the destination device.
According to the present invention,.when a repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to a destination device connected to the repeater, demodulating means in the repeater demodulates the received communication data to device data synchronized with the device reference clock set in the destination device, and then phase information extracting means extracts a phase information added at the time of modulation by using an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation, and then transmitting means transmits the demodulated communication data to the destination device.
Therefore, by extracting the phase information, the communication data modulated to synchronize with the transmission reference clock can be demodulated to the device data precisely synchronized with the device reference clock set in the source device without performing a processing of sinning bits. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in a source device.
Further, to attain the above object, according to still further aspect of the present invention, there is provided a transmission system constructed by interconnecting a plurality of repeaters, each having at least one device connected thereto, by a transmission line, for exchanging digital data between devices, between repeaters, or between a device and a repeater, each of the plurality of repeaters comprising: modulating means for modulating device data to communication data synchronized with the transmission reference clock, when the device data synchronized with the device reference clock set in a source device connected to the repeater is output from the source device, the transmission reference clock being the basis for an exchange of communication data between repeaters and being set to an appropriate value in advance with reference to a plurality of device reference clocks set in at least one device; phase information adding means for adding a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation by the modulating means, a number of bits of each unit block of the communication data synchronized with the transmission reference clock and a number of bits of each unit block of plural device data synchronized with the plurality of device reference clocks respectively being set to appropriate values in advance with reference to frequencies of the plurality of device reference clocks and a frequency of the transmission reference clock; first transmitting means for transmitting the communication data modulated by the modulating means to a predetermined destination; demodulating means for demodulating received communication data to device data synchronized with the device reference clock set in a destination device connected to the repeater, when the repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to the destination device; phase information extracting means for extracting the phase information added at the time of modulation by using the empty area which is equivalent to the difference between the number of bits of each unit block of the device data and the number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation by the demodulating means; and second transmitting means for transmitting the communication data demodulated by demodulating means to the destination device.
According to the present invention, when a repeater receives the device data synchronized with the device reference clock set in a source device connected to the repeater from the source device, modulating means in the repeater modulates the device data to communication data synchronized with the transmission reference clock, and then phase information adding means adds a phase information to be used to demodulate the modulated communication data into device data, to an empty area which is equivalent to a difference between a number of bits of each unit block of the device data and a number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of the modulation, and then first transmitting means transmits the modulated communication data to a predetermined destination by the repeater. Conversely, when a repeater receives communication data modulated to synchronize with the transmission reference clock and addressed to a destination device connected to the repeater, demodulating means in the repeater demodulates the received communication data to device data synchronized with the device reference clock set in the destination device, and then phase information extracting means extracts the phase information added at the time of modulation by using the empty area which is equivalent to the difference between the number of bits of each unit block of the device data and the number of bits of each unit block of the communication data synchronized with the transmission reference clock, at the time of demodulation, and then second transmitting means transmits the demodulated communication data to the destination device.
Therefore, by adding the phase information, the device data synchronized with the device reference clock set in the source device can be modulated to the communication data synchronized with the transmission reference clock without performing a processing of bit interpolation. Further, by extracting the phase information, the communication data modulated to synchronize with the transmission reference clock can be demodulated to the device data precisely synchronized with the device reference clock set in the source device without performing a processing of sinning bits. As a result, digital data can be transmitted truly and precisely from an input unit to an output unit having a different sampling rate from that of the input unit.
In a preferred embodiment of the present invention, the phase information comprises a phase difference between a block synchronous signal of communication data synchronized with the transmission reference clock and a synchronous signal of a device reference clock set in the source device.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.